The rated voltage, the range of the fluctuating voltage, and other factors of an AC power line vary from region to region. For example, the rated voltages vary among countries, such as 100V and 115V.
For many electronic instruments energized with alternating current, voltage changes must be limited severely. If such instruments energized with alternating current are used in other regions having different power supply ratings, it is necessary either to modify the specifications of the instruments according to the ratings or to connect a power regulator.
If the design of an instrument is modified according to the power ratings in the regions where the instrument is used, printed-wiring boards and various components included in the instrument can no longer be used in common because of the modification of the power rating. Therefore, other components must be prepared according to the modified power ratings. As a result, the manufacturing costs increase, as well design costs. Also, a heavy burden is imposed to control over components and the manufacturing yield deteriorates.
One conceivable method of solving the above-described problems is to use power regulators. This method permits standardization of instruments. However, since the ratings differ among regions or countries as described above, power regulators having wide control ranges, i.e., expensive power regulators, are needed. Where voltages fluctuate within wide ranges, they are often employed at low efficiencies and hence operate inefficiently. In addition, the system is made large and complex. Furthermore, the maintenance costs and the running costs are increased.